There are numerous situations in which a semiconductor component is bonded to a substrate. In one common example, the semiconductor component is bonded or attached to a thermally conductive heat sink. In order to extract waste heat generated during device operation and to provide electrical contact, semiconductor components are attached to a thermally conductive heat sink substrate, usually by a means of a solder. The surface of the substrate is metalized to allow adhesion of the solder if the substrate is not composed of a metal. The surface of the substrate is generally metalized to control the interaction between the solder and the substrate.
Failure of semiconductor components is accelerated in part by mechanical stress. One source of stress results from the different coefficient-of-thermal-expansion (CTE) between the material of the semiconductor component and the material of the substrate. At temperatures where the solder is molten, the mechanical stress is insubstantial. Once the temperature decreases below the melting temperature of the solder, the substrate applies a mechanical stress on the component that is proportional to the difference in the CTE of the semiconductor and the substrate as well as the difference between the melting temperature of the solder and the temperature of the component.
There are several procedures to minimize the mechanical stress on the component due to the soldering process:                a. Choose a substrate whose CTE is close in value to the CTE of the semiconductor component        b. Choose a solder with a low melting temperature        c. Choose a solder that remains malleable in the solid form.        
One factor to be considered in the first procedure is that substrate materials, e.g. molybdenum (Mo) and copper-tungsten (Cu10W90), whose CTE is close in value to the CTE of common semiconductor components, e.g. silicon (Si), gallium arsenide (GaAs), and indium phosphide (InP), have relatively poor values of thermal conductivity (TC) relative to copper or diamond. The performance and reliability of a semiconductor component decreases with increasing temperature. Substrates with lower values of TC result in higher operating temperatures for semiconductor components.
Some of the factors to be considered in the second and third procedure are:                a. The melting temperature of the solder, e.g. indium, is sufficiently high (156° C.) to result in a significant mechanical stress        b. Malleable solder migrates under thermal cycling, spatial variations of temperature and electrical current        c. Molten solder reacts uncontrollably with the metallization of the semiconductor component or the substrate, often resulting in compounds or alloys with undesirable material properties.        d. The melting of solder reduces the thickness precision of the bond.        e. Molten solder may wick        
There is a need for improved methods for bonding that introduce less mechanical stress.